Multitasking makes you tired so, in the end, you end do less.
When we attempt to multitask, we don’t actually do more than one activity at once, but quickly switch between them. And this switching is exhausting. It uses up oxygenated glucose in the brain, running down the same fuel that’s needed to focus on a task.
“That switching comes with a biological cost that ends up making us feel tired much more quickly than if we sustain attention on one thing,” says Daniel Levitin, professor of behavioral neuroscience at McGill University. “People eat more, they take more caffeine. Often what you really need in that moment isn’t caffeine, but just a break. If you aren’t taking regular breaks every couple of hours, your brain won’t benefit from that extra cup of coffee.”
This is one of the reasons I don’t ask job applicants if they can “multitask,” and one of the reasons I’m suspicious of people who claim they can.